Media application basics

Media application basics

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Appears in: Media

Working with media often requires changing the characteristics of media files, such as bitrate or resolution. Finding a straightforward way to get started can be pretty intimidating. On this page, you will learn about the tools used and how to install them quickly.

First, we describe the basic usage for two common command-line media utilities: Shaka Packager and FFmpeg and then we help you quickly get the tools installed. Why cover two applications? While both are powerful and useful by themselves, neither does everything needed to prepare media for the web. We also created the Media conversion and Media encryption pages which show many more common operations with these two applications.

These applications aren't the only options available for file manipulation tasks, but they are two of the most common and powerful. Other options include the GUI applications Miro, HandBrake, and VLC. There are also encoding/transcoding services such as Zencoder, Amazon Elastic Encoder, and Google Transcoder API (currently in beta).

You'll notice in what follows that the word 'resolution' doesn't appear. What the two applications output are just the dimensions; the numbers themselves. That's because resolution is just an informal shorthand for the dimensions of a video. In every case that follows, We talk about specific numbers.

Shaka Packager #

Shaka Packager is a free media packaging SDK. If you were using a media player on your site, Shaka Packager is what you would use to prepare the files. It supports conversion for the two most common video streaming protocols: Dynamic Adaptive Streaming over HTTP (DASH) or HTTP Live Streaming (HLS). Shaka Packager supports key security features: common encryption and Widevine digital rights management (DRM). It can also handle live-streaming, and video-on-demand.

Despite what it says on the package, this utility is for more than C++ developers. You can use it as both a library for building media software and as a command-line utility for preparing media files for web playback. It's the latter capacity that's useful for us here. In fact, for web media creators, Shaka Packager is the only way to do some tasks without spending money on expensive commercial applications.

Here's the basic pattern for a Shaka Packager command:

packager stream_descriptor [stream_descriptor-2 [stream_descriptor-n]] [flags]

This isn't quite what you get if you type packager -help. This example is easier to reason about, and this reflects the examples in the Shaka Packager documentation. Note that there are multiple stream_descriptor items in the pattern. Though we don't show it, you could manipulate the video and audio streams of a file separately in a single command.

Compare this basic pattern with a simple use that displays file characteristics. In the example, We've lined up equivalent parts.

packager stream_descriptor [stream_descriptor-n] [flags]

packager input=glocken.mp4 --dump_stream_info

The command outputs this:

File "glocken.mp4":
Found 2 stream(s).
Stream [0] type: Video
codec_string: avc1.640028
time_scale: 30000
duration: 300300 (10.0 seconds)
is_encrypted: false
codec: H264
width: 1920
height: 1080
pixel_aspect_ratio: 1:1
trick_play_factor: 0
nalu_length_size: 4

Stream [1] type: Audio
codec_string: mp4a.40.2
time_scale: 48000
duration: 481280 (10.0 seconds)
is_encrypted: false
codec: AAC
sample_bits: 16
num_channels: 2
sampling_frequency: 48000
language: eng
seek_preroll_ns: 20833

Look for the characteristics discussed in Media file basics and notice a few things. The height and width are correct for full HD, and the audio and video codecs are among the preferred codecs for their container types, AAC for audio and H264 for video. Notice also that streams are identified with numbers. These are useful for operations that manipulate the audio and video separately.

Notice that the output above doesn't show the bitrate. Despite what's missing, this output is easier to read, so we use it whenever we can. When we need information that Shaka Packager can't get, such as the bitrate, we use FFmpeg.

FFmpeg #

FFmpeg is also a free application for recording, converting, and streaming media files. Its capabilities aren't better or worse than Shaka Packager's. They're just different.

The basic pattern for an FFmpeg command looks like this:

ffmpeg [GeneralOptions] [InputFileOptions] -i input [OutputFileOptions] output

Like Shaka Packager this application can handle multiple streams. Some of its options are used in multiple locations and manipulate the file output differently depending on where they are in the command. Be aware of this as you look at FFmpeg questions on Stack Overflow and similar sites.

We'll again compare the basic pattern to the example for displaying file characteristics.

    ffmpeg [GeneralOptions] [InputFileOptions] -i input        [OutputFileOptions] output

ffmpeg -i glocken.mp4

In addition to the information we requested, this also prints an error message as shown in the example below. That's because this is technically an incorrect usage of FFmpeg. We use it because it displays information we care about.

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'glocken.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.17.100
Duration: 00:01:47.53, start: 0.000000, bitrate: 10715 kb/s
Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc), 1920x1080, 10579 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 59.94 tbc (default)
Metadata:
handler_name : VideoHandler
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
handler_name : SoundHandler
At least one output file must be specified

Installing applications with Docker #

If you plan to follow along and try our commands you could either install the required tools manually, or take the easy path and use Docker. We suggest using Docker, because this is going to save you a lot of time. On top of that we've provided the instructions to get you set up quickly.

  1. Start by creating a new directory somewhere on your computer named media-tools; you can use whatever name you like, just note that the following instructions assume you are using media-tools as the directory name.

  2. Create a docker and media directory inside of media-tools. This will keep your media directory out of the build context. This is important because media is where files are stored that we plan to do operations on, and some of them could be quite large. Putting the Dockerfile directly in media-tools would slow down building the image if you ever rebuild it down the road—perhaps to change the versions installed.

  3. Create /media-tools/docker/Dockerfile, and add the following build instructions:

    FROM google/shaka-packager:release-v2.4.3 as packager
    FROM jrottenberg/ffmpeg:4.3.2-alpine38
    COPY --from=packager /usr/bin /usr/bin
    ENTRYPOINT ["sh"]
  4. Build the image:

    docker build -t media-tools ./docker
  5. Run the image as an interactive shell. On Linux:

    docker run -w /media -v ${PWD}/media:/media -it --rm media-tools
    /media #

    On Windows:

    docker run -w /media -v %cd%/media:/media -it --rm media-tools
    /media #
Gotchas!

Make sure you run the previous docker commands from inside the media-tools directory.

While running the image you can check versions for both FFmpeg and Shaka Packager to validate everything was successful by running ffmpeg -version and packager --version. The output should look like this:

/media # ffmpeg -version
ffmpeg version 4.3.2 Copyright (c) 2000-2021 the FFmpeg developers
built with gcc 6.4.0 (Alpine 6.4.0)
configuration: --disable-debug --disable-doc --disable-ffplay --enable-shared --enable-avresample --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-gpl --enable-libass --enable-fontconfig --enable-libfreetype --enable-libvidstab --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libxcb --enable-libx265 --enable-libxvid --enable-libx264 --enable-nonfree --enable-openssl --enable-libfdk_aac --enable-postproc --enable-small --enable-version3 --enable-libbluray --enable-libzmq --extra-libs=-ldl --prefix=/opt/ffmpeg --enable-libopenjpeg --enable-libkvazaar --enable-libaom --extra-libs=-lpthread --enable-libsrt --enable-libaribb24 --extra-cflags=-I/opt/ffmpeg/include --extra-ldflags=-L/opt/ffmpeg/lib
libavutil 56. 51.100 / 56. 51.100
libavcodec 58. 91.100 / 58. 91.100
libavformat 58. 45.100 / 58. 45.100
libavdevice 58. 10.100 / 58. 10.100
libavfilter 7. 85.100 / 7. 85.100
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 7.100 / 5. 7.100
libswresample 3. 7.100 / 3. 7.100
libpostproc 55. 7.100 / 55. 7.100
/media # packager --version
packager version v2.4.3-dd9870075f-release

Now that you've tried your hand at using Shaka Packager and FFmpeg, you can continue learning the basic concepts, next up Media streaming basics.

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